The present invention relates to a method for preparing norbornene and substituted derivatives of norbornene via the Diels-Alder reaction.
The described method comprises reacting a cyclic diene with an olefinic compound to yield norbornene or a substituted derivative of norbornene.
The present invention also relates to a polymer prepared by polymerizing a monomer prepared by the method of the invention in the presence of a catalyst and another monomer.
Norbornene and substituted norbornene compounds are used for the preparation of such compounds as cycloolefine-copolymers (COC). These copolymers may be prepared, for example, by introducing a norbornene derivative in a metathesis-ring-opening polymerization reaction or reacting norbornene with ethene or an other alpha-olefine in the presence of a vanadine based Ziegler-Natta catalyst or a metallocene catalyst.
It is essential in all of these polymerization reactions that the cyclic monomer is pure. Especially polyunsaturated impurities (such as the trimer or dimer of cyclopentadiene) are adverse, because they cause cross-linking in polymers. Other polycyclic impurities (such as tetracyclododecene compounds) may also have adverse effects, because they cause polymer chains to be of greater rigidity than norbornene and substituted norbornene compounds, thereby causing the properties of the polymers to be prepared to become different from those achieved when pure products are used for polymerization. Furthermore, it should be pointed out that the diastereomers (exo and endo forms, respectively) of norbornene compounds have a different effect on polymer compounds; the exo form yields more rigid polymers than the endo form. From the point of view of further use of the monomer, the product should contain as much as possible of the desired diastereomer. Usually, one attempts to achieve as high as possible a concentration of the exo diastereomer.
Because mixtures of cycloolefin compounds are difficult to purify by distillation, it is preferable to synthesize them under conditions, in which the desired norbornene or substituted cylcoolefin compound (the endo or exo diastereomer of substituted norbornene or the corresponding tetracyclododecene compound) are in as pure a form as possible.
Among the substituted norbornene derivatives, e.g. phenylnorbornene (5-phenyl-bicyclo-[2.2.1]-hept-2-ene) and indanylnorbornene (1,4-methano-1,9a,4,4a-tetrahydrofluorene) are known organic compounds. They have been prepared in a batch process by using a solvent and starting compounds in equimolar ratios. This requires a very long reaction time if a high yield and a pure product are desired. Elevation of the reaction temperature can be used to shorten the reaction time, but at the same time the product yielded turns out to be very impure (the reaction mixture contains large amounts of the trimer and tetracyclododecene compounds). On the other hand, maintaining a low temperature and extending the reaction time causes the undesired endo form to become the predominating diastereomer.
Some solutions to these problems have been suggested in the known art. Nippon Zeon has performed the synthesis of phenylnorbornene by using a large excess of styrene as the solvent (EP-A2-0 345 674) and Mitsui Sekka has developed a method for the isomerisation of the endo diastereomer into the exo diastereomer (EP-A1-0 499 226). It is not possible to use these methods either for the preparation of pure products with high yields.
DE Published Patent Application No. 2 161 215 discloses a process for preparing 5-vinylnorbornene-2. According to this known process cyclopentadiene is slowly added to a mixture of butadien and di-tert-butyl-p-cresol. The reaction is interrupted after 60 minutes, when 20% of the cyclopentadiene has reacted. The yield of vinylnorbornene is only 71.6% and the reaction mixture obtained is rather impure containing a mixture of cyclopentadien, dicyclopentadien, butadiene, 5-vinylnorbornene-2 bicyclonoadiene, vinylcyclohexene and residues with higher boiling points.
The object of the present invention is to overcome the shortcomings of known techniques and to provide an entirely new method for the preparation of norbornene and substituted norbornene derivatives.
The invention is based on the idea of synthesizing norbornene compounds via a Diels-Alder reaction while maintaining a low or relatively low concentration of the cyclic diene. According to the invention, this is achieved by introducing a cyclic diene into the reaction with an olefinic compound gradually during the reaction to keep the concentration of the cyclic diene low during the reaction. The reaction is continued until essentially all (at least 80%, preferably at least 95% and in particular at least 99%) of the calculated amount of cyclic diene has reacted.
The norbornene or substituted norbornene compounds obtained can be used for preparing polymers.
More specifically, in the present method, the cyclic diene is added gradually during the reaction.
The polymer according to the present invention is prepared by polymerizing a monomer prepared by the above described synthesis in the presence of a catalyst alone or in the presence of another monomer.
The present invention provides considerable advantages. The described method of the invention enables one to achieve a very pure product, high yield, short reaction time and, if desired, high concentrations of the exo diastereomer. Thus, after the reaction, the concentration of unreacted cyclic diene reactant in the reaction mixture is typically less than 3.0 wt-% and the concentration of the undesired trimer of the diene less than about 0.10 wt-%. It is even possible to achieve reaction mixtures that contain practically no residues of unreacted diene and no detectable amounts of trimer.